Power transmissions are employed in vehicle powertrains to provide a plurality of ratios between the power source, such as an engine, and the final drive mechanism, such as a differential. These transmissions have taken on many forms including mechanically shifted or manual step ratio transmissions, planetary step ratio transmissions, and continuously variable power transmissions.
The continuously variable power transmissions generally include an adjustable belt drive, adjustable drive rollers, hydrostatic motor pump drives, or electrical power drives. The power split transmission also includes one or more planetary gearsets.
In more recent developments, it is proposed to use input-split power transmissions, output-split power transmissions, or compound-split power transmissions. Each of these power split type transmissions incorporate planetary gearsets.